Method and apparatus for relieving hobs



Sept. 13, 1932. E. c. HEAD mmnon AND APPARATUS FOR RELIEVING u OBSOriginal Filed May '16 1928 3 Sheets-Sheet l INVENTOR. Zr7zasi 65 6402 ATTW Sept. 13, 1932. E. c. HEAD 1,877,174-

METHOD AND APPARATUS FOR RELIEVING 30135 Original Filed May 16, 1928 3Sheets-Sheet 2 44/ 67 154 70 T Ft 3 42 1 2 T 1517 I la 4 4 143 A 131 444' o o 3 j 152 w m 81 1 130 w 1 143 O '78 v 7 87 w 130 9/ 131 8A 159I32 138 136 150 Y 90 135- v 137 85152 58 126 82 83 12 1:4 81 :1 6 l 5INVENTOR. 4

[W2 5i C [faal Sept. 13, 1932. E. 0. HEAD 1,877,174

METHOD AND APPARATUS FOR RELIEVING HOBS Original Filed May 16. 1928 5Sheets-Sheet 3 IN VEN TOR.

limesi C fiai B l5 ATM Patented Sept. 13, 1932 UNITED STATES PATENTOFFICE ERNEST 0. HEAD, OF ROCHESTER, NEW YORK, ASSIGNOR TO GLEASONWORKS, QF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK MET OD ANDAPPARATUS r03. RELIEViNG irons Original application filed May 16, 1928,Serial No. 278,208, and in Great Britain April 29, 1929. Divided i andthis application filed April 24, 1930. Serial No. 447,011.

The present invention relates to a method and toapparatus for relievlnggear-cuttmg hobs and particularly hobs for cutting spiral bevel gears.

This application is a division of my pending application, Serial No. 278,208, filed May 16, 1928, covering a hob.

One object of this invention is to provide a relieving method, andapparatus for practicing the same, through which it will be possible toproduce a gear cutting hob which will have the same cutting action aftersharpening as when new.

A further object of this invention is to provide a method forrelievingtaper hobs and apparatus for practicing the method, by which the teethat the small end of the hob can be made stronger than taper hobs ofprevious constructions.

A still further object of this invention is to provide apparatus foraccomplishing the above mentioned purposes of the invention which may beemployed as a simple and inexpensive attachment to a conventional formof lathe.

Other objects of the invention will be apparent hereinafter from thespecification and from the recital of the appended claims.

In the drawings:

Figure 1 is a side elevation and Figure 2 an end elevation of a latheequipped with a relieving attachment constructed according to oneembodiment of this invention and showing the same employed in relievinga taper hob.

Figure 3 is a fragmentary plan view, on an enlarged scale, of the lathe,showing particularly the relieving attachment;

Figure 4; is a section on. the line &-4 of Figure 3;

Figure 5 is a diagrammatic view illustrative of the relieving method,showing the rel-- ative movement that takes place between the relievingtool and the hob blank during the movement of the tool from one end ofthe hob to the other;

Figure 6 is a diagrammatic view further illustrative of the relievingmethod, showing the relative movement which takes place between therelieving tool and the hob blank during the relieving of the hob; and 7I Figure 7 is an axial sectional view of a taper hob relieved accordingto the method of. this invention.

The cutting edges of a hob are'arranged in a helical thread, the teethofthe hobbeing formed by gashing and relieving this thread. After a hobis sharpened the new cutting edges have changed positions in the threadhelix, that is, they have different angular and axial positions from thepositions previously occupied by the cutting edges. The prior practicehas been to relieve the teeth of a hob so that the side faces of theteeth are of the same pressure angle from front to rear. It will beclear that when such a hob is sharpened the new cutting edges will haveaxial andangular positions di'fl'erent from the axial and angularpositions of the original cutting edges, and that consequently thecutting action of the new cutting edges will be different from thecutting action of the original cutting edges. While the pressure anglesof the original cutting edges were correct for producing a gear of adesired pressure angle, the pressure angles of the new cutting edgeswould not be correct for producing the same gear.

One of the purposes of the present invention is to provide a methodwhereby a gear cutting hob may be relieved so that its cutting actionwill be just as correct after sharpening as it was before sharpening. Tothis end, in manufacturing a hob according to this invention, therelieving tool is tilted continuously during the relieving of each toothof the hob so as to vary continuously the inclination of the cuttingedge of the relieving tool relative to the tooth face being relieved,thus varying the pressure angle of the side face of the toothcontinuously from front to rear of the tooth. This variation in pressureangle of the tooth from front to rear is just enough to insure that whenthe hob is sharpened, its cutting edges will have pressure anglesexactly suited, by reason of their changed positions in the helix, toproduce the required pressure angle on the teeth of the gear to be cut.

one of the teeth of In a further aspect, the present invention has forits purpose to provide a method for relieving taper hobs whereby taperhobs, such as are employed in the cutting of spiral bevel gears, may beproduced which are much stronger than taper hobs of previousconstructions. This purpose is achieved by tilting the relieving toolcontinuously as it moves from the large to the small end of the hob soas to provide teeth on the hob of continuously increasing pressure anglefrom the large to the small end of the hob. Thus, the teeth of the smallend of the hob, being of greater pressure angle than corresponding teethin prior constructions, will be correspondingly stronger. The pitch ofthe hob thread can be maintained constant, if desired, on its root,pitch, top, or any other surface by rotating the blank at a uniformvelocity and moving the tool longitudinally of the hob at a uniformvelocity and by tilting the tool during its longitudinal movement aboutpoints lying in one or other of these surfaces.

The two features of this invention may be used separately or incombination. Thus, a hob may be relieved so that it has teeth with sidefaces of changing inclination from front to back or so that it hascutting edges of changing pressure angle from one end of the hob to theother or the hob can be relieved in such a way as to have both cuttingedges of changing pressure angle from one end of the hob to the otherand teeth with side faces of changing pressure angle from front to rear.

This invention relates only to the relieving of the side faces of thehob teeth. The tips of the teeth may be relieved in any usual orsuitable manner.

In the embodiment of the invention illustrated in the accompanyingdrawings, the relieving movements are imparted to the tool and as thetool reciprocates, the hob blank is simultaneously rotated on its axisand the tool moved lengthwise of the blank to relieve the successiveteeth correctly and in accordance with their helical arrangement. Thesemotions are usual in hob-relieving machines.

The invention is illustrated in connection with the relieving of a taperhob. In the relieving of such a hob, it is required to feed therelieving tool toward the hob blank continuously, as the tool moves fromone end to the other of the hob, in order to maintain the tool inoperative relation to the hob. This feed motion is preferably effectedin a direction perpendicular to the cone surface of the hob to preventslippage between the side of the tool and the sides of the teeth beingrelieved.

Where the hob is tapered, it is desirable not only that the side facesof the hob teeth be relieved so as to be of changing pressure angle fromfront to rear so that the hob can be sharpened without altering itsaccuracy, but

also that hob have cutting edges of continuously increasing pressureangle from the large to the small end of the hob so as to get increasedstrength at the small end of the hob. The first of these objects isaccom- 4 plished in the embodiment of the invention illustrated by usingthe relieving motion of the tool to tilt the tool continuously duringthe relieving of each tooth of the hob and the second of these objectsis achieved by using the motion required to feed the tool relative tothe hob in accordance with the taper of the hob, to tilt the relievingtool continuously as it moves from one end of the hob to the other.

In the drawings, the invention is illustrated as embodied in anattachment for a usual form of relieving lathe and the mechanisms of thelathe ordinarily provided for rotating the hob blank, producing therelieving movement and feeding the relieving tool lengthwise of the hobare employed for the same purposes in the present invention.

Referring first to Figures 1 to t inclusive, 10 indicates thework-piece, the hob to be relieved, in this case, a taper hob such asmight be employed in bobbing spiral bevel gears. The hob blank ismounted between the centers L0 and 41 carried by the head stock 4:2 andthe tail stock 43, respectively, of the 43 is slidably adjustable. Theconstruction of the head and tail stocks and the adjustment of thelatter form no part of the pres ent invention and may be of any usual orsuitable type.

The work is rotated continuously, during the operation of the machine,being driven from one of the cone pull ys 4&6 by means of the drivingdog designated generally at d7.

The relieving tool is designated by the numeral 34-. It is mounted, in amanner to be described more particularly hereinafter, upon a carriage 50which slides on the horizontal ways or guides 51 provided upon the topof the bed or frame The table or carriage 50 is moved longitudinally ofthe bed or frame 45 in time with the work rotation, by means of a screw52 which threads into a nut 53 securedto the carriage 50.

The screw 52 is driven from the head stock spindle 54 through the gears55, 56, the shaft 57, the gears 58, 59, 60, the shaft 61, and the gears62, 63, 64 and 65, the last named gear being secured to the screw shaft52.

l/Vhere a taper hob is to be relieved, it is preferred, as stated above,to mount the relieving tool 34 so that it moves in its reliev ingmovement in a direction perpendicular to the cone surface of the worlrwhereby, as described in my co-pending application No. 202,695, filedJune 30,1927, any tendency gularly adjustable plate 67.

of the relieving tool to slip sidewise, during relieving, due to theconical nature of the plate 67 which is angularly adjustable on "thecarriage 50 and which is provided with an annular flange 68 that seatsin a circular grooveor socket 69 provided in the uppe 3 face of thecarriage 50. The relieving tool is carried on this plate 67 and, hence,by adjusting the plate 67 to the required angle, the relieving tool canbe positioned to move in a direction perpendicular to the cone stir--face of the hob 10.

7 moves longitudinally of the work-piece 10,

to maintain the tool at all times in operative engagement with theconical hob blank. For this reason, the carrier 70 is provided. This ismounted for sliding movement on the an- This carrier 70 is guided in itsmovement on the plate 67 by means of the ways 71 which engage adovetailed guide surface formed on. the plate 67.

The mechanism for feeding the carrier 7 and with it the relieving tool,toward the hob blank during the movement of the carriage will now bedescribed. Secured to. one side of the bed or frame 45 of the I machineis a bracket 73 and on this bracket is mounted an angularly adjustableguideplate 74. The guide-plate 74 is provided with a stud 75 thatengages in a suitable socket or recess formed in the bracket 7 3 and1,1,. it is about the axis of this stud 75 that the guide-plate 74 isangularly adjusted on the bracket 73. This adjustment of the'guideplateis made manually and the guide-plate can be secured in any adjustedposition on f the bracket 73 by means of bolts 76 which pass througharouate slots 7 7 formed in the guide-plate concentric with the stud 75and thread into the bracket 7 3. Graduations 78 are provided on anarcuate flange formed j at the edge of the bracket 73 and the guide-jplate 7 4 has an index mark 79 scribed on its upper face at itsperiphery to assist in setting the guide-plate accurately to an anglecorresponding to the angle of taper of the ,1 hob 10.

There is a dove-tailed guide-rail 80 formed on the upper face of theguide-plate 74 and this guide-rail 80 is engaged by correspondlnglyshaped surfaces of a slide or follower 81. The follower 81 is connectedthrough the relieving tool 34 mounted thereon will be fed in toward thework as the carriage 50 moves longitudinally on the bed or frame 45.Thus, the relieving tool will be maintained automatically andcontinuously in operative engagement with the hob 10 despite the taperof the cone surface of the hob. Due to the angular setting of the plate67, this movement of the carrier 7 0 will at the same time take place ina direction perpendicular to the cone surface of the hob 10.

Mounted-on the carrier 70 for reciprocable movement relative thereto isthe relieving slide 85. This slide 85 is reciprocated by means of asnail cam 87, such as is ordinarily employed in a relieving lathe. Thiscam acts to feed the relieving tool 34 toward the hob as each tooth ofthe hob rotates beneath the relieving tool and then allows the relievingtool to return quickly to starting position ready for the succeedingrelieving operation on the next tooth of the hob. The snail cam 87 issecured to the vertical shaft 88 which is ournaled in the extension 83of the carrier 70. The cam engages a contact member or. follower 89which is secured to the slide 85. A pair of springs 90, which aremounted upon rods 91 secured to the part 83 and slidable in the slide85, serve to maintain the surface of the cam 87 at all times in contactwith the contact member 89 and to return the slide 85 quickly to initialposition after each tooth of the hob has been relieved.

The relieving cam 87 is driven continuously during the operation of themachine and in timed relation with the rotation of the work-piece 10 andthe movement of the carriage or table 50 so that the proper relievingoperation is imparted to the successive teeth of the hob. The mechanismfor so rotating the cam 87 will now be described.

Mounted on the shaft 61 (Figure 1) at its inner end is a spur gear 95'forming one of a set of change gears 95, 96 and 97 which transmit therotation of the shaft 61 to the shaft 98 suitably journaled in the bedor frame 45 of the machine. Thus, through the gears 95, 96 and 97, theshaft 98 is rotated in timed relation with the rotation of the work 10.This shaft 98 carries at its inner end a bevel gear 99 forming one of aset of differential gears of which the planet members 100 are mountedupon a spider 101 which is secured to the shaft 102 journ aled in thebase or frame of the machine 45 in alignment with the shaft 98. Theother side gear 103 of the differentia-l is journaled on the shaft 102and is rotated in timed relation with the rotation of the lead-screw 52,being driven from the leadscrew 52 by means of the change gears104, 105,106 and 107, the shaft 108, the bevel gears 109 and 110, the shaft 111,the worm 112, and the worm wheel 113 which is secured to or formedintegral with the side gear 103. From the construction described, itwill be seen that the shaft 102is driven continuously in timed iio . 121(Figure 4).

relation with the work rotation and table movement.

The shaft 102 carries at its outer end a spur gear 115 which forms oneof a set of change gears 115, 116, 117, and 118 whlch serve to transmitthe motion of the shaft 102 to a shaft 120 which extends longitudinallyof the machine between the sides of the bed or frame 45 and to which iskeyed a bevel gear This bevel gear 121 meshes with and drives a bevelgear 122 on a vertical shaft 123 which is journaled in the table orcarriage 50 co-axial with the flange 68 of the plate 67.

Secured to the shaft 123 at its upper end is a bevel gear 124 whichmeshes with a bevel gear 125 that has a splined connection with theshaft 126. The bevel miter gear 125 is suitably journaled in the plate67 while the shaft 126 is suitably journaled adjacent its outer end inthe carrier 70. Keyed to the shaft 126 at its outer end is a bevel gear127 which meshes with and drives a bevel gear 128 that is secured to thecam shaft 88. Through the mechanism just described, it will be seen thatthe cam 87 is rotated continuously during the operation of the machinein timed relation with the work rotation and carriage movement.

So far, the means for rotating the work, the means for moving thecarriage or table 50, the angular adjustment of the relieving tool, themeans for imparting a feed movement to this tool in a directionperpendicular to the cone surface of the Work and the means forimparting the relieving movement to the too]. have been described. Ishall now describe the means for continuously tilting the tool duringthe relieving of the teeth of the hob and as the tool moveslongitudinally from one end to the other of the hole.

The relieving tool 34 is secured by means of straps 130 and bolts 130 toan angularly movable plate 131. This plate 131 is mounted upon a slide132 for pivotal movement about the axis of the stud 133 which isjournaled in the slide 132. The slide 132 is adjustable by means of thescrew 135 upon a second slide 136 which, in turn, is adjustable by meansof a screw 137 upon the relieving slide 85. The ustments effected bymeans of the screws 135 and 137 are in directions at right angles toeach other and permit of adjusting the relieving tool for relieving hobsof different diameters and of different pitches.

The plate 131 is provided with an extension or arm 138 and thisextension or arm is provided on its upper face with fine clutch teethadapted to be engaged by similar clutch teeth on the lower face of anarm 139. This arm 1.39 is provided with a slot 140 in its outer end andin this slot is adjustably mounted a roller 141. The roller 141 engagesa guide rail 142 (Figures 1 and 3) which is secured to the carriage 5O.By engaging the clutch teeth of the arm 138 and the arm 139, the arm 139can be connected to the plate 131.

The guide-rail 142 is straight in the machine shown and extends parallelto the axis of the work. As the guide-rail is inclined to the path ofmovement of the relieving slide 85, it follows that during the relievingof each tooth of the hob, the support 131 and the relieving tool 34carried thereby are moved angularly on the slide 132 thereby tilting therelieving tool relative to the side face of the hob tooth being relievedas the hob tooth rotates past the cutting edge of the relieving tool.Thus, the pressure angle of the side face of the tooth of the hob ischanged constantly from front to rear of the tooth and so the hob isrelieved in such a manner that it will always have the same cuttingaction on the tooth of a gear.

It follows, also, that as the guide surface of the rail 142 is inclinedto the path of movement of the carrier 70, the support 131 and relievingtool 34 will be given a continuous angular movement as the relievingtool moves from one end of the hob to the other thereby producing on thehob cutting edges of changing pressure angle from one end of the hob tothe other. By adjusting the slide 136 so that the axis of the stud 13.3lies in the pitch surface of the hob, the angular tilting movement ofthe relieving tool 34 will take place about points lying in the pitchsurface of the hob and consequently the hob will be of constant pitchfrom one end to the other measured on that surface. In like manner, thehob might be made of constant pitch on the root surface or any othersurface thereof.

A spring 143 secured at one end to the arm 139 and at its other end tothe guide-rail 142 serves to maintain the roller 141 at all times incontact with the guide-rail.

Figures 1, 3 and 4 show the relieving tool 34 positioned for relievingone side of the hob thread. The opposite side of the thread may berelieved by substituting an appropriate relieving tool and bydisconnecting the arm 139 from the plate 131 and connecting instead withthe plate 131 another arm 145 shown in dotted lines in Figure 3. Thisarm 145 extends beneath the hob to the other side of the machine andlike the arm 139 is provided with a slot 140' in which is adjustablymounted a roller 141 which is adapted to engage the inner face of aguide-rail 142 that is secured to the carriage or table 50 in a mannersimilar to the guide-rail 142. A coil-spring 143' may be employed tomaintain the roller 141 in engagement with the guide-rail 142. Throughthe guide-rail 142', the roller 141, the arm 145 and the plate 131, theproper tilting movements can be imparted to the relieving tool torelieve the other side of the hob thread to produce side cutting edgeson that side of varying pressure angle from one end of the hob to theother and relieved side tooth surfaces of varyingpressure angle fromfront to rear of the hob teeth.

The action of the relieving tool is clearly illustrated in Figures 5 and6. As the hob rotates on its axis, the relieving tool is movedcontinuously toward and away from the hob, moving toward the hob duringthe passage of each tooth 11 of the hob under the tool and being movedquickly away from the hob again after the tool has cleared a tooth sothat the tool will be in position to engage the follow ing tooth of thehob. As the relieving tool 34 is fed into the tooth of the hob, it issimultane ously tilted through the engagement of the roller 141 or 141,as the case may be, with the guide 142 or- 142'. Thus,.the angle ofinclin ation of the cutting edge of thetoolto the axis of the hob willbe changed as the tool moves from front to rear of the tooth 11. Hence,the sides of the teeth of the hob will be of changing inclination orpressure angle from front to rear. By suitably locatingithe guidesurface 14.2 or making it of proper curvature, therefore, teeth, canb'eproduced on the hob having side surfaces so inclined to the axis ofthe hob that the pressure angle of the cutting edges after sharpening,will be changed just enough from the pressure angles of the originalcutting edges to compensate for the changed position of the cuttingedges 7 place about points 37, 37', etc., lylng on the due tosharpening.

Figure shows in full lines and in dotted lines two positions assumed bythe relieving tool 34 as it relieves the sidetooth surface 36 of thetooth 11 of the hob 10. The movement of the tool toward the blankprovides the necessary side. clearance for cutting and the tilt ing ofthe tool during this movement provides the tooth face 36 with acontinuously varying pressure angle from front to rear of such amountthat after the hob tooth is sharpened, the new cutting edges will havepressure angles varied just enough from the pressure angles of theoriginal cutting edges .to compensate for the changed position of thecutting edges in the helical surface of the hob thread.

As the carrier 'ZO moves continuously in a direction inclined to theguidesurface 142 or 142, as the case may be, during the relieving of thehob, the tilting motion imparted to the relieving tool will becontinuous from end to end of the hob. Hence, the inclination of thesidecutting edge 35 of the relieving tool relative to the side faces ofthe hob teeth being relieved varies continuously as the tool moveslongitudinally of the hob. In this way side tooth surfaces are producedon the hob which are of continuously varying prlessure angle from oneend of the hob to the ot 1G1.

In producing a taper hob for the purpose of cutting spiral bevel gears,the pressure angles of the cutting edges are preferably in creased fromthe large to the small end of thehobso as to provide teeth at the smallend ofthe hob of-increased strength. ,In Figure,

the cutting edge 35 of'the tool to the hob;

thread has been increased with the conse-, quence'that the tooth 21 ofthe hob will have, a side cutting edge 19 of increased pressure;

angle as compared with the pressure angle of the sidecutting' edge 16 ofthe hob tooth 17 For'the pur'poseof comparison, the position of the toolrelative to the blank when relieving the tooth l7z-is shown in dottedlines at 34 i at, the right hand side of Figure 5 to indicate how thetool has been tilted continuously to the postion 34', shown in fulllines, which is the position it has assumed when it reachesthe tooth 21.As will be understood, the tilting motion of the tool is continuous asthe tool moves longitudinally of the hob' from one end to the other sothat the pressure angles of cor.- responding side cutting edges of thehob vary continuously from one-end of the hob to the other.

As stated above, if the tilting motion takes pitch surface 15 of thehob, the pitch 79 of the hob can be made uniform on this surface asshown. So a hob relieved'according to the present invention may beemployed for cut ting spiral bevel gears according to the processof theTrbojevich Reissue Patent No. v

16,17 3" of September 22, 1925, or the process of the Taylor Patent No.1,618,240 of February 22,1927, etc. v

As stated above, the guide surface of the rails 142 and 142 are straightand extend parallel to the axis of the work. When the" guide-rail is setat the correct distance from the axis of the work, it has been foundthat this straight guide surface will impart the correct tiltingmovement to the relieving tool to properly change the pressure angles ofthe cutting edges of the hob during the relieving of the hob teeth. Theguide surface may, however, be curved or inclined to the axis of the hobas may be determined by the'distance' of the guide surface away from theaxis of the hob and by the amount of movement required to impartsuflicient tilting movementto the tool as it moves from endto end of thehob to vary the pressure angles of'the cutting edges the desired amount.

In the case of a cylindrical hob for cutting spur gears, there wouldordinarily be no object in changing the pressure angle of the cut tingedges from one end of the hob to the other and in relieving such a hob,neither the Plate 6 01 hecarrier 70 would have any an i gularadjustment. The relieving tool would move perpendicular to the pitchsurface of the hob, namely, perpendicular to the axis of the hob. Inthis case, the tilting movement of the tool required to properly relieveeach of the teeth of the hob according to this invention would beobtained by selecting a guide member 1 12 or 142 which has its guidingsurface inclined at the proper angle to the axis of the hob. Thus, sucha hob could be relieved so that each of its teeth would'have side facesof changing inclination to the axis of the hob from front to rear butthe cutting edges of the hob would be of the same pressure angle fromone end of the hob to the other. The hob would, therefore, be suited tocut spur gearsand would be of the same accuracy after sharpening as whennew.

Figure 7 shows a taper hob relieved accord- 2 ing to this inventionwhere the two features of changing inclination of the side faces of thehob teeth from front to rear and of changing pressure angle of thecutting edges of the hob from one end of the hob to the other arecombined. Such a hob would be relieved with the attachment shown in thedrawings and with the plate 67 and carrier adjusted at an angle to theaxis of the hob determined by the cone angle of the hob. 14: designatesthe axis of the hob, 15 its pitch cone surface, and 13 is a pitch coneapex. Due to the method of relief, the pressure angles of the hob teethwill vary continuously from one end of the hob to the other. Thus, thepressure angle a of the cutting edge 16 of the hob tooth 17 will be lessthan the pressure angle a of the opposite side cutting edge 18 of thesame tooth and these two pressure angles in turn will be less than thepressure angles a and a of the corresponding side cutting edges 19 and20, respectively, of the hob tooth 21 at the small end of the hob. Thepressure angles of the cutting edges of the teeth 22, 23, 2 1 and 25intermediate the teeth 17 and 21 will be greater than the pressureangles of the cutting edges of the tooth 16 and less than the pressureangles of the cutting edges of the tooth 21, the pressure angles of thecutting edges of each of the teeth 22, 23, 24 and 25 depending upontheir position along the length of the hob, the cutting edges of the hobincreasing continuously by reason of their relief from one end of thehob, to the other. Each tooth of the hob will have side faces of varyingpressure angle, that is, of varying inclination to the axis of the hob,from front to back, as already explained with reference to Figure 6 andas already ex plained, the pitch of the hob can be made constant fromone end of the hob to the other on any surface of the hob, such as thepitch surface 15.

It will be understood, also, that the present invention is not limitedto the formation of hobs of constant pitch, as with the present invention it is possible to change the pressure angles of theside faces ofthe teeth of a hob of varying pitch from front to rear so that the hobwill always have the same cutting ing from one end of the hob to theother so that it increases towards the small end of the hob, it ispossible to use a conical grinding wheel with which to relief-grind. Theincrease in pressure angle of the teeth at the small end of the hobpermits of relieving the successive teeth of the hob with a grindingwheel without danger of interference with other teeth. I

While the invention has been described in connection with a particularembodiment and in connection with a particular use for that embodiment,it will be understood that the invention is capable of various furthermodi fications and uses without departing from its scope and thisapplication is intended to cover any adaptations, uses, or embodimentsof the invention following, in general, the "principles of the inventionand including such departures from the present disclosure as come withinknown or customary practice in the art to which it pertains and as maybe applied to the essential features hereinbefore set forth and as fallwithin the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. The method of relieving a hob which comprises effecting a relativerelieving movement between a relieving tool and hob blank for each toothof the hob while rotating the hob blank on its axis and moving therelieving tool and blank relative to one another longitudinally of theblank and tilting the relieving tool as it moves from one end of the hobto the other to cause the tool to produce teeth on the hob having sidecutting edges of changing pressure angle from one end of the hob to theother.

2. The method of relieving a hob which comprises effecting a relativerelieving move ment between a relieving tool and the hob blank for eachtooth of the hob while rotating the hob blank on its axis and moving therelieving tool and blank relative to one another longitudinally of theblank and simultaneously changing the inclination of the side cuttingedge of the relieving'tool to the axis of thehob blank continuouslyduring the relieving of the side faces of each tooth of the hob and asthe relieving tool moves from one end of the hob blank to the other.

his

- dinally of the hob to present successive teeth of the hob to theaction of the relieving tool, and while relieving the side faces of eachtooth of the hob, tilting the relieving tool continuously to produceside faces on 'the hob teeth of changing inclination from front to rear.

4.. The method of relieving a hob which comprises rotating a hob blankon its axis at a uniform velocity while producing a relative movementbetween the blank and relieving tool longitudinally ofthe hob at auniform velocity topresent successive teeth of the hob to the action ofthe relieving tool, and

while relieving the side faces of each tooth of the hob, tilting therelieving tool continuously to produce side faces on'the hob teeth ofchanging inclination from front to rear. v

5. The method of relieving a taper hob which comprises tilting thecutting edge of the relieving tool continuously during the relieving ofthe side faces of. each toothfof the hob and as the relieving tool movesfrom one end of the hob to the other whereby to produce teeth on the hobhaving side faces of continuously changing pressure angle from front torear and having side'cutting edges of continuously changing pressureangle from one end of the hob to the other. 6 The method of relieving ataper hob i Whichcomprises producing relative relieving movementsbetween the hob blank and the relieving tool to relieve side faces ofsuccessive teeth of the hob while rotatingthe hob blank on its axis andsimultaneously producing ar-elative movement between the blank andrelieving toollongitudinally of the blank to present successive teeth ofthe hob to the action of the relieving tool, and simultaneously tiltingthe'relieving tool con tinuously as it moves from one end ofthe hob tothe other to produce side cutting edges ofcontinuously changing one endof the hob to the other.

7. The method of relieving ajtaper hob which comprises producingrelative relieving movements"betweenthe hob blank and the relieving toolto relieve the side faces of successive teeth of the hob whilerotatingthe blank on its axis at a uniform velocity andsimultaneouslyproducing a relative movement between the blank and relieving toollon'gitudinallyof the hob at a uniform velocity to presentsuccessiveteeth of the hob to .the action of the relieving tool, andsimultaneously tiltingthe relieving tool continuously as it moves fromone end ofjthe hobto the other to produce side cutting edges ofcontinuously" changing pressure angle from one end of the hob to theother.

i 8. The method of relieving a taper hob pressure angle from whichcomprises producing relative relieving movements between the hob andrelieving tool to relieve the sides of successive teeth of the hob whilerotating the hob blank on its axis at a uniform velocity andsimultaneously producing a relative movement between the hob blank andthe relieving tool longitudinally of the blank at a uniform velocity topresent successive teeth of the hob to the action of the relieving tooland changing the inclination of the side cutting edge of the relievingtool to the axis of the hob continuously during the relieving of sidefaces of successiveteeth of the hob and as the tool moves from one endof the hob blank to the other.

v9. The method of relieving'a taper hob which consists in producingrelative relieving movements between a relieving tool and the hob blankwhile rotating the blank on its axis continuously at a' uniformvelocity, producing a relative movement between the tool and blanklongitudinally of I the hob blank at a uniform velocity and feeding therelieving tool relative to the blankin accordance with the taper ofthehob, and simultaneously varying the inclination of the side cutting edgeof the relieving tool relative to the axis of the hob blank whereby toproduce cutting edges on the hob of varyingpressure angle from one endofthe hob to the other.

10. The method of relieving a taper hob which comprises producinga'relative relieving'movement between a relievin'g'tool-and the hobblank while rotating the blank on its axis continuously, simultaneouslyproducing a relative movement between the hob blank 7 and the relievingtool longitudinally of the blank to present successive teeth of'theblank to the action of the relieving tool and simultaneously producing arelative feeding move inentbetween the relieving tool and the blank in adirection perpendicular itothe'con'e sur face of the blank continuouslywhile the tool is moving from one end of the blank to the other, andchanging the inclination of the side cutting edge of the relieving toolto the axis ofithe blank continuously asit moves from one end of theblank'to' the other.

support, a rotatable work support, a car-' r age upon which one of saidsupports is mounted, means for moving the carriage lon 11. In apparatusfor relieving hobs, a tool .115

ments, and means for varying the inclination of the side cutting edge ofthe relieving tool relative to the axis 'of'theworkj continu ouslyduring the relieving of the side faces of each'hob tooth.

12; In apparatus for relieving taper hobs,

atool support, arotatable"work'support, a

carriage upon which one of said supports is mounted, means forpositioning the tool support so that it will move in a planeperpendicular to the cone surface of the work, means for moving thecarriage longitudinally of the work, means for rotating the work supporton its axis, means for simultaneously producing a relative relievingmotion between the tool support and the work in timed relation with thework and carriage movements, means for imparting a relative feedmovement between the tool support and the work in a directionperpendicular to th cone surface of the work as the carriage moveslongitudinally, and means for changing the inclination of the sidecutting edge of the re lieving tool to the axis of the work continuouslyduring the relieving of the side faces of each tooth of the hob.

13. In apparatus for relieving hobs, a tool support, a rotatable worksupport, a carriage upon which one of said supports is mounted, meansfor moving the carriage longitudinally of the work, means for rotatingthe worl support on its axis, means for imparting a relieving motion tothe tool support in timed relation with the work and carriage movements,and means actuated by said relieving movement for changing theinclination of the side cutting edge of the relieving tool relative tothe axis of the work continuously during the relieving of the side faceof each tooth of the hob.

14. In apparatus for relieving taper hobs, a tool support, a rotatablework support, a carriage upon which one of said supports is mounted,means for moving the carriage longitudinally of the work, means forrotating the work support on its axis, means for imparting arelievingmovement to the tool support in timed relation with the workand carriage movements, means for simultaneously producing a relativefeed movement between the tool and work in accordance with the taper ofthe cone surface of the hob, and means actuated by the said feedmovement for changing the inclination of the side cutting edge of therelieving tool to the axis of the work continuously as it moves from oneend of the work to the other.

15. In apparatus for relieving hobs, a bed, a reciprocable tool slide, arotatable work spindle, a carriage upon which the tool slide isreciprocable, said carriage being movable on the bed in a directionlongitudinal of the work, a tool support rotatably mounted on the slideand adapted to carry a relieving tool, means for moving the carriagelongitudinally of the work, means for rotating the work spindle on itsaxis, means for imparting a relieving movement to the tool slide intimed relation with the work and carriage movements, and means actuatedby the movement of the tool slide, during the relieving of each toothofthe hob,for moving the tool support on its axis to change theinclination of the side cutting edges of the relieving tool relative tothe axis of the work continuously during the relieving of the side facesof each tooth of the work.

16. In apparatus for relieving hobs, a bed, a reciprocable tool slide, arotatable work spindle, a carriage upon which the tool slide isreciprocable, said carriage being mounted on the bed for movement in adirection longitudinal of the work, a tool support rotatably mounted onthe slide and adapted to carry a relieving tool, means for moving thecarriage longitudinally of the work,.means for rotating the work spindleon its axis, means for imparting a relieving movement to the tool slidein timed relation with the work and carriage movements, a guide securedto the carriage, and a follower carried by the tool support adapted toengage said guide, said guide being so formed that the relievingmovement of the slide causes a movement of the tool support on its axisto change the inclination of the side cutting edge of the relieving toolcontinuously to the axis of the work during the relieving of each toothof the hob.

17. An attachment for a lathe provided with a bed, a rotatable workspindle, a slidable carriage movable on the bed in a directionlongitudinal of the work, means for moving the carriage, means forrotating the work spindle, and a shaft driven in timed re lation withthe work spindle and carriage movements, comprising a reciprocable toolslide, a tool support rotatably mounted on said slide, means driven fromsaid shaft for reciprocating said slide, and means adapted to beactuated by movement of said slide for moving said tool support on itsaxis to change the inclination of the side cutting edge of the relievingtool relative to the axis of the work continuously during the relievingof each tooth of the work.

18. An attachment for a lathe provided with a bed, a rotatable workspindle, a slidable carriage movable on the bed in a directionlongitudinal of the work, means for moving the carriage, means forrotating the work spindle, and a shaft driven'in timed relation with thework spindle and carriage movements, comprising a reciprocable toolslide, a tool support rotatably mounted on said slide, means driven fromsaidshaft for reciprocatingsaid slide, and means adapted to be actuatedby the movement of said carriage for moving said tool supportcontinuously on its axis to change the inclination of the. side cuttingedge of the tool continuously relative to the axis of the work duringthe relieving of the side faces of each tooth of the worl 19. Inapparatus for relieving taper hobs,

a bed, a reciprocable tool slide, a rotatable work spindle, a carriagemovable in adiupon which one of rection longitudinal'of the work, a toolsup port rotatably, mounted on the slide and adapted to carry arelieving tool, a, carrier uponwhich the slide is-reciprocable, a plateuponwhichthe carrier is movable, said plate being mounted on saidcarriage for angular adjustment thereon to position the tool slide -andcarriage for movement in a direction perpendicular to "the cone surfaceof the work, means for rotating the work spindle on its axis, means forimparting movement to the carriage, means for moving the carrier, meansfor reciprocating the tool slide, a guide on the carriage, and afollower carried by the tool support adapted to engage said guidewhereby movement of the tool carriage acts to move the tool supportcontinuously during movement of the carriage to change the inclinationof the side cutting edge of the relieving tool continuously relative tothe axis of the work as the tool moves from one end of the work to theother.

20. In apparatus for relieving hobs, a tool support, a rotatable worksupport, a carriage upon which one of said supports is mounted, meansfor moving the carriage longitudinally of the work, means for rotatingthe work support on its axis, means for imparting relieving movementsbetween the tool and work supports in timed relation with the work andcarriage movements, and means for changing the inclination of the sidecutting edge of the relieving tool to the axis of the work as the toolmoves relatively from one end of the work to the other to produce teethon the hob having cutting edges of changing pressure angle.

21. In apparatus for relieving hobs, a tool support, a rotatable worksupport, a carriage said supports is mounted, means for moving thecarriage longitudinally of the work, means for rotating the work supporton its axis, means for. imparting relieving movements between the tooland work supports in timed relation with the work and carriage movementsand means for changing the inclination of the side cutting edge of therelieving tool to the axis of the work both as the tool relieves eachtooth of the hob blank and as the tool moves relatively from one end ofthe work to the other whereby to produce teeth having side faces ofchanging pressure angle from front to rear and side cutting edges ofchanging pressure angle from one end of the hob to the other.

22. In apparatus for relieving hobs, a tool support, a rotatable worksupport, a carriage upon which one of said supports is mounted, meansfor moving the carriage longitudinally of the work, means for rotatingthe work support on its axis, means for imparting re-f lieving movementsbetween the tool and work supports in timed relation with the work andcarriage movements, and means actuated by movement of the carriage forchanging the hobs,

the work support on its axis, meansfor imparting relieving movementsbetween the tool and work supportsqln timed relat on with the work and;C11T1tg6 movements,

meansoperative on movement of the carriage forproducing a relative feedmovementubetween the tool and work to maintain the. tool in operativerelation with the conical. blank as it moves relatively from one endthereof to the other, and means operative during'feed movement forchanging the inclination of the side cutting edge'of the tool to theaxis of the work during relieving of= difierent teeth of the hob wherebytovproduce teeth on'the hob sure angle from one end thereof totheother'.

24;. In apparatus for relieving taper hobs. a tool support, a rotatablew'orksupport, a carriage upon which one of said supports is mounted,means for moving thecarriage longitudinally of the; work,-means forrotating the work support'onlits axis, means forim: partingrelievingmovements between the tool and work supports in timed relationwith the work and carriage movements, means for a;

producing a relative-feedmovement between the tool and work to maintainthe tool'in op,- erative relation with the conical blank as the toolmoves relatively from one end of the work to the other and'means for.changing the inclination of the side cutting edge of the tool to theaxis of the work during relieving ofdifierent teeth-of the hob blankwhereby to produce teeth on thehob having side zcutting edges of varyingpressure angleirom g one end of the hob tothe other. 1

25. In apparatus'afor relieving hobs,"a tool support, a rotatable worksupport, a carriage upon which one of said supports is mounted,

means for moving the carriage longitudinal- 1y of the work, means forrotatingthe work support on its axis, means for imparting re lievingmovements between the tool and work supports in timed relation with theworkand carriage movements, means whereby the relieving movement of: thetool operates to tilt thBliOOl continuously during relieving of eachtooth of the hob blank, and meansactuated 'bymovement of the carriagefor fur-f 'ther tilting the relieving tool continuously as it movesrelatively. from one end ofthe work to the other,

7 26,111 apparatus for relievingtaper'hobs, a tool support, a rotatablework support,-a-

carriage upon which one of said supports'fis having side cuttingedges-of varyingpresmounted, means for moving the carriagelongitudinally of the work, means for rotating the work support onitsaxis, means for imparting relieving movements between the tool andwork supports in timed relation with the work and carriage movements,means for producing a relative feed movement between the tool and worksupports to maintain the tool in operative relation with the conicalblank as it moves relatively from one end of the blank to the other,means whereby the relieving movement of the tool operates to tilt therelieving tool continuously during the relieving of each tooth of theblank, and means operative during the feed movement for further tiltingthe relieving tool during relieving of different teeth of the hobwhereby to produce teeth on the hob having side cutting edges of varyingpressure angle from one end of the hob to the other.

27. In apparatus for relieving hobs, a bed, a carriage mounted on thebed for movement longitudinally thereon, a rockable tool support and awork support, one of said supports being mounted on the bed and theother on the carriage, means for rotating the work support, means foreffecting movement of the carriage, a guide mounted on the bed, and

means operatively connecting the guide with the tool support whereby onmovement of the carriage, the tool support is rocked on its axis tochange the inclination of the side of the tool to the axis of the workto produce .v cutting edges of different pressure angle on differentteeth of the hob.

' 28. In apparatus for relieving hobs, a bed, a carriage mounted on thebed for movement longitudinally thereon, a slide reciprocable on thecarriage, a tool support rockably mounted on the slide, a work supportrotatably mounted on the bed, means for effecting movement of thecarriage, a guide mounted on the carriage, means for reciproeating theslide to impart relieving move- 4.5

ments to the tool and means operatively connecting the guide with thetool support whereby on movement of the slide, the tool support isrocked to produce side faces of changing pressure angle from front torear on the teeth of the hob.

29. In apparatus for relieving taper hobs, a bed, a work supportrotatably mounted on the bed, a carriage mounted on the bed for movementaxially of the work support, a plate angularly adjustable on thecarriage, a carrier reciprocable on the plate, a slide reciprocable onthe carriage, a tool support rockably mounted on the slide, a guideangularly adjustable on the bed, means operatively connecting the guideto the carrier to produce a feed movement of the tool support relativeto the work support to maintain the tool in operative relation with theconical blank as it moves relatively to one end thereof to the other, aguide mounted on the carriage, means work. ERNEST C. HEAD.

